The present invention relates to a filter apparatus provided in a pipeline for conveying a fluid to remove solid impurities from the fluid. More particularly, the present invention relates to a filter apparatus suitable for use in a supply line for an abrasive liquid used in a chemical/mechanical polisher (CMP) for semiconductor substrates. The present invention also relates to a method of regenerating a filter unit.
With the rapid progress of the technology to fabricate high-integration semiconductor devices in recent years, circuit wiring patterns or interconnections have been becoming increasingly small and fine, and spaces between wiring patterns have also been decreasing. As the wiring spacing decreases, the depth of focus becomes shallower in circuit pattern formation by photolithography or the like. Accordingly, surfaces of semiconductor wafers on which circuit pattern images are to be formed by a stepper require a higher degree of surface flatness.
FIG. 15 shows a conventional polishing apparatus for making the surface of a semiconductor wafer flat. The apparatus has a polishing table 4 with a polishing cloth 2, for example, bonded to the surface thereof to form a polishing surface. The apparatus further has a substrate holder 6 for holding a substrate W to be polished, e.g. a semiconductor wafer. With an abrasive liquid Q being supplied between the polishing surface and a surface of the substrate W that is to be polished from an abrasive liquid supply pipe 8, the substrate W is pressed against the polishing surface with a predetermined pressure by the top ring 6, and while doing so, the polishing surface and the substrate W are caused to slide relative to each other to perform polishing. Such a polishing apparatus performs mechanical polishing using an abrasive liquid as a polishing fluid, and in some cases, it also performs polishing accompanied by a chemical action using an alkaline or acidic polishing solution.
In an abrasive liquid supply system of such a polishing apparatus, abrasive grains may agglomerate to form particles in the pipeline. If supplied to the surface to be polished, such particles cause flaws, known as scratches, on the surface to be polished. Accordingly, it is conceivable to equip the pipeline with a filter apparatus for trapping particles larger than a predetermined size in the supplied fluid. In such a filter apparatus, as shown in FIG. 16, filter units fa and fb are connected to branched pipelines, which are branched off from the abrasive liquid supply pipeline, through respective joints (not shown), so that when a predetermined processing time has elapsed, the used filter unit fa or fb can be replaced without stopping the abrasive liquid supply line.
However, in a case where filter units are connected to the pipeline through joints as stated above, it is necessary to conduct an operation of detaching and reattaching bolts and nuts when the filter units are replaced. The efficiency of the operation is unfavorably low because the abrasive liquid scatters. Moreover, abrasive grains in the abrasive liquid remaining in the branched pipeline that is not used may agglomerate to form particles.